1. Field of the Invention
The present invention relates to a constant-pressure mechanism and a constant-torque mechanism used, for example, in a contact measuring apparatus or the like.
2. Description of the Related Art
As well known, for example, in a measuring apparatus such as a dial gauge or the like, a contact (measuring member) is pressed against a surface to be measured by a force of a coil spring so that measurement is carried out. However, in a configuration where the contact is pressed by the coil spring simply, the urging force of the coil spring varies depending on its deflected state. Therefore, there is a problem that the contact pressure varies whenever the contact moves.
That is, when the urging force of the coil spring varies in conjunction with a quantity of movement of the contact, the contact pressure of the contact against the surface to be measured varies on all such occasions. As a result, by a reaction force corresponding to the contact pressure, the surface to be measured per se may be deformed, or the state where the subject to be measured is supported may be changed, so that it is impossible to obtain a proper result of measurement or a reproducible result of measurement.
Therefore, in the related art, a constant-pressure mechanism for urging a contact with a substantially constant force that is independent of a quantity of movement of the contact has been proposed, for example, in JP-A-54-160266. That is, in this constant-pressure mechanism, without using such a coil spring the elastic force of which is changed in conjunction its displacement quantity, a contact is fixed to a pneumatic piston so as to be urged by the pressure of an air chamber on which a constant air pressure acts.
According to such a related constant-pressure mechanism, it is possible to keep the measuring pressure of a contact substantially constant independently of a quantity of movement of the contact. It is however necessary to dispose a base portion of the contact in the inside of an air chamber in which the air pressure is kept constant. Therefore, the structure for supporting the contact becomes so large in size that it is inconvenient to handle the constant-pressure mechanism, or the constant-pressure mechanism is an obstacle for measurement in a narrow space.
Further, although a mechanism for obtaining a constant torque has been proposed in JP-Y-5-21324, this constant-torque mechanism is intended for a screw driver. Therefore, the mechanism is so complicated that it is impossible to apply the mechanism to a simple measuring apparatus such as a caliper gauge.